Hi Peggy, I am still planning a holding tank for my Rhodes Reliant, more enlightened by reading your book GET RID OF BOAT ODORS. I also got a reasonable quotation from C.C. Tech, following your recommendation. For venting the tank, I like your idea of 2 vents, around 1". The question is, exactly where to put them. I'm thinking about leading one up to the cabin top, maybe integrating it with a dorade vent and adding a solar fan. That's about 3 feet up, with about two 90 degree bends. For the other, I have three choices: It could go sidewise, out the hull, pretty short and direct. My concerns about this are that a clamshell on the topsides under the rail would be aesthetically disruptive and vulnerable in docking situations. Also if noxious odors come from that vent, they could blow into the cockpit area when the wind is from the wrong direction. A second choice is to go to the cabin top again. My fear is that noxious odors would come into the cockpit. The third choice involves going up and then below the deck back to the stern and exiting under the counter, below the transom, about 12-15 feet. I'd prefer the third choice, if it will provide adequate venting and not create hose odors for its full length. What is yor recommendation? Many thanks, Ben Stavis ben.stavis@verizon.net
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filter
many folks use an air filter. they are sold in most marine stores. be careful to get the one that fits your hose diameter. i just installed one in my vent hose. my vent is under the setee, through the hanging locker in the v-berth, and up just beneath the deck level. it terminates with a very small cowl vent that is barely noticeable. people say it eliminates 100% of the odor from the holding tank. i haven't had mine long enough to vouch for that. it is my belief that the shortest run, with the least bends is best. rt
many folks use an air filter. they are sold in most marine stores. be careful to get the one that fits your hose diameter. i just installed one in my vent hose. my vent is under the setee, through the hanging locker in the v-berth, and up just beneath the deck level. it terminates with a very small cowl vent that is barely noticeable. people say it eliminates 100% of the odor from the holding tank. i haven't had mine long enough to vouch for that. it is my belief that the shortest run, with the least bends is best. rt
The only workable choice is your first one...
Out the side, as short and straight as possible. With a 1" diameter, less than 3' long, you should only need one. An open bulkhead thru-hull (not a "vent fitting") that matches your gelcoat color will be unnoticeable...if necessary, you can paint it and any clamshell to match. As for any vulnerability during docking, I've never heard from anyone for whom that's an issue. Both the other options you describe will actually create the odors you're trying to prevent. However, we do need to discuss the best location for the tank before specifying where the vent should go. Why do I have a strong suspicion that you're an engineer?
Vent filters also create the very problem they're sold to solve (why couldn't I have invented something that does that???)...by blocking the exchange of air through the vent needed to keep the tank aerobic--which is what is needed to prevent odor from occurring in the first place, and therefore eliminates the need to filter it. Filters are also EXPENSIVE--$50+ each--and only last a season at most...and that's only if they don't get wet...a filter is "toast" immediately if it gets wet, which happens too easily on sailboats due to waste spilling into the vent while the boat is heeled...which can also clog it up. A filter also makes it impossible to backflush the vent line to clear out any waste in it before it can create a blockage. So yes...filters DO trap most, if not all, odor out the vent...but there are other ways to accomplish that which are much cheaper and don't create more problems than they solve.
Out the side, as short and straight as possible. With a 1" diameter, less than 3' long, you should only need one. An open bulkhead thru-hull (not a "vent fitting") that matches your gelcoat color will be unnoticeable...if necessary, you can paint it and any clamshell to match. As for any vulnerability during docking, I've never heard from anyone for whom that's an issue. Both the other options you describe will actually create the odors you're trying to prevent. However, we do need to discuss the best location for the tank before specifying where the vent should go. Why do I have a strong suspicion that you're an engineer?
Vent filters also create the very problem they're sold to solve (why couldn't I have invented something that does that???)...by blocking the exchange of air through the vent needed to keep the tank aerobic--which is what is needed to prevent odor from occurring in the first place, and therefore eliminates the need to filter it. Filters are also EXPENSIVE--$50+ each--and only last a season at most...and that's only if they don't get wet...a filter is "toast" immediately if it gets wet, which happens too easily on sailboats due to waste spilling into the vent while the boat is heeled...which can also clog it up. A filter also makes it impossible to backflush the vent line to clear out any waste in it before it can create a blockage. So yes...filters DO trap most, if not all, odor out the vent...but there are other ways to accomplish that which are much cheaper and don't create more problems than they solve.Reply to discussion on vents
Hi Peggy, You asked about the location of the holding tank. You can see the layout of my boat at: http://astro.temple.edu/%7Ebstavis/rr/interior.gif A photo of a sistership's head also will give you a sense of the geometry: http://astro.temple.edu/%7Ebstavis/rr/unknowninterior.htm You see the head is amidships to port. I'm planning the holding tank under the lockers outboard of the sink and head. The bottom of the tank will be a few inches above the floor. The top of the tank will be at sink counter height, a few inches above the water line. I can fit in a custom shaped 30 gallon tank and still have the locker space, although some of the locker space will be used by valves and a discharge pump. As I re-read your book, I see that a big part of the problem is to remove heavier-than-air gasses from the holding tank. The higher the vent tube goes, the more difficult this is. For a tank in this location, even if I put the vent through the topsides, I would still loop it up to the deck and then sidewise and down a bit, like an engine exhaust, so there still would be a couple of feet of vertical distance. I think this is the circumstance where your book suggests dual vent lines for cross ventilation and/or mechanical means of forcing air through the tank. I'm now thinking that I might put one vent up to the cabin top, with a solar powered vent fan to force air into the tank. I might put a second vent that would come out on the side of the trunk cabin, with a clamshell facing aft, as an exhaust vent. This should provide an air flow through the tank. I'm not an engineer, but I've been maintaining, updating, and restoring this particular boat for 40 years. I want to make this installation work well. If it doesn't, I'll get the nasty complaints from the admiral and I'll have the job of fixing it. Do you think my plan will be OK? Many thanks, Ben Stavis ben.stavis@verizon.net
Hi Peggy, You asked about the location of the holding tank. You can see the layout of my boat at: http://astro.temple.edu/%7Ebstavis/rr/interior.gif A photo of a sistership's head also will give you a sense of the geometry: http://astro.temple.edu/%7Ebstavis/rr/unknowninterior.htm You see the head is amidships to port. I'm planning the holding tank under the lockers outboard of the sink and head. The bottom of the tank will be a few inches above the floor. The top of the tank will be at sink counter height, a few inches above the water line. I can fit in a custom shaped 30 gallon tank and still have the locker space, although some of the locker space will be used by valves and a discharge pump. As I re-read your book, I see that a big part of the problem is to remove heavier-than-air gasses from the holding tank. The higher the vent tube goes, the more difficult this is. For a tank in this location, even if I put the vent through the topsides, I would still loop it up to the deck and then sidewise and down a bit, like an engine exhaust, so there still would be a couple of feet of vertical distance. I think this is the circumstance where your book suggests dual vent lines for cross ventilation and/or mechanical means of forcing air through the tank. I'm now thinking that I might put one vent up to the cabin top, with a solar powered vent fan to force air into the tank. I might put a second vent that would come out on the side of the trunk cabin, with a clamshell facing aft, as an exhaust vent. This should provide an air flow through the tank. I'm not an engineer, but I've been maintaining, updating, and restoring this particular boat for 40 years. I want to make this installation work well. If it doesn't, I'll get the nasty complaints from the admiral and I'll have the job of fixing it. Do you think my plan will be OK? Many thanks, Ben Stavis ben.stavis@verizon.net
We need to talk...
There's too much detail specific to your particular installation to be practical in a discussion forum...I'll email you.
There's too much detail specific to your particular installation to be practical in a discussion forum...I'll email you.
Exiting out the side one a sailboat
Ben, I'm very interested in hearing how you resolve this issue as I am in the same position with my 1970s vintage Pearson 39. If I mount the one inch thruhull on the side, I'll need to keep it lower than just under the toe rail to keep it from acting like a rub rail. My only concern is taking on a little salt water when I heel... and this boat likes to heel. Mike
Ben, I'm very interested in hearing how you resolve this issue as I am in the same position with my 1970s vintage Pearson 39. If I mount the one inch thruhull on the side, I'll need to keep it lower than just under the toe rail to keep it from acting like a rub rail. My only concern is taking on a little salt water when I heel... and this boat likes to heel. Mike
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